The problem only appears when the shopping card icon is enabled in the settings. Apparently IE7 (and older Firefox) don't support the inline-block, seems a likely suspect.
=== modified file 'uc_cart/uc_cart_block.css'
--- uc_cart/uc_cart_block.css 2009-02-06 21:40:54 +0000
+++ uc_cart/uc_cart_block.css 2009-02-17 21:07:08 +0000
@@ -1,13 +1,45 @@
/* $Id:$ */
-#block-cart-title-bar {
+/**
+ * Styles for the cart block icon.
+ */
+.cart-block-icon-full, .cart-block-icon-empty {
+ display: inline-block;
+ padding: 2px 12px 8px 12px;
+ height: 7px;
+}
